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(No Model.)

B. P. CLARK. SAFETY DEVICE FORDYNAMOS.

No. 426,108. Patented Apr. 22, 1890.

Fig I k i J w/msssas; INVENTOH Ernest Clark UNITED STATES PATENT OFFICE.

ERNEST P. CLARK, OF NE\V YORK, N. Y., ASSIGNOR TO THE CLARK ELECTRICCOMPANY, OF SAME PLACE.

SAFETY DEVICE FOR DYNAMOS.

SPECIFICATION forming part of Letters Patent No. 426,108, dated April22, 1890. Application filed December 30, 1889' Serial No, 335,298. (Nomodel.)

To all whom it may concern.-

Be it known that I, ERNEST P. CLARK, a citizen of the United States,residing in New York city, in the county of New York and State of NewYork, have invented certain new and useful Improvements in SafetyDevices for Dynamo-Electric Machines, of which the following is aspecification.

In the operation of shunt-wound dynamos designed for a constant currentwith varying electro-motive force for the purpose of supplying arclights in series or other similar purpose a difficulty sometimes arisesfrom the characteristic action of such a machine, I 5 which tends toincrease the eleetro-motive force of the dynamo whenever from any causethe resistance of the circuit is increased. With such machines, if themain circuit is broken by accident or otherwise, the electromotive forceof the dynamo rises at once and in a few seconds becomes much greaterthan the normal working electro-motive force. This action renders thebroken line very dangerous to persons or animals coming in contact withit. At the same time the increased elect-romotive force may becomeinjurious to the in sulation of the dynamo-coils, If, now, the brokenline should be joined again, it would practically have the effect ofplacing the dynamo on short circuit, as the dynamo is generating a veryhigh electro-motive force and all the lamps or other devices included inthe circuit are in their condition of lowest resistance. The result ofclosing the line (by accident or otherwise) at such a time is to causean enormous rush of current and great strains on the armature and shaftof the d ynamo, which may even be great enough to wreck the machine. Ifan automatic regulator is used in connection with such a dynamo, theresults are really worse, for the reason that the regulator of such amachine operates to increase the electro-motive force when theresistance rises, and thus maintains 4 5 a constantcurrent with varyingelectro-motive force. If the main circuit of a dynamo provided with sucha regulator is broken, the result is an immediate rise of electronnotiveforce to the utmost limit that the machine is capable of producing.

The object of this invention is to provide a means for throwing thedynamo out of action in the event of a rupture of the main circuit, andto accomplish this result without danger to the dynamo and quicklyenough to prevent any considerable rise in its electro-motive force.

The invention is illustrated in the accom= panying drawings, in which-Figure 1 represents a general diagram of the circuits and apparatusused; and Fig. 2 represents a detail of a portion of the apparatus. I

A represents a dynamo elcotric machine whose main circuit is B and whosefield-magnets are in the shunt-circuit O. The shuntcircuit also includesa switch-arm c and a regulator C. The switch-arm is fitted with acontact-shoc c, which normally bears upon a contact-piece 0 A spring 0is attached to the arm 0 in such a manner that it tends to draw it overagainst the stop-pin c to break the shunt-circuit, In making thismovement the shoe 0 is brought momentarily into connection with a secondcontact-piece a This throws a circuit D containing a resistance (Z intothe shunt-circuit for a purpose which will be explained later. There isalso connected with the switch-arm the piston-rod of an air-cushion c..This is arranged so that So the first movement of the arm to break thecircuit will be rapid; but immediately the motion is retarded while theshoe is passing over the second contact. The switch-arm is maintained inits normal position by a latch c, which is pivoted at e. and carries onone end a hook which engages with the arm and 011 the other end asoft-iron bar constituting the armature of a magnet E, included in themain circuit of the dynamo. So long as the 0 magnet is sufficientlyenergized the armature is held up and locks the switch-arm; but when themagnet becomes de-energized or abnormally weakened the armature drops ofits own weight, or by reason of a spring a and releases the switch arm.

The core of magnet E is made hollow and a push-rod e placed therein, bywhich the armature may be driven away from the pole of the magnet Theoperation of the device is as follows: As long as the main circuit isintact and the IOC current flowing therein is nearly or quite normal thelatch and switch remain as shown; but if now the main circuit is broken,or for any reason the main current is very much decreased, the latch cis no longer held in posit-ion by the magnet, but drops, releasing thearm 0, which is drawn by the spiral spring toward the stop-pin, thusbreaking the fieldmagnet circuit and throwing the dynamo out of action.If this were all the action of the device there would be a serious areformed when the arm 0 left the contact 0 and the extra current producedby suddenly breaking the field-magnet circuit would be liable to rupturethe insulation of the field-coils. To avoid this action the secondcontact 0 is introduced in the path traversed by the arm 0,

which second contact is connected in the shunt through the coil of highresistance, as hereinbefore described. The extra current is thereforedischarged through this coil. The movement of the arm from contact 0 tocontact 0 being rapid, the air in the cushion becomes compressed andretards the movement of the arm. This retardation is aided by theweakened condition of the spring, and the arm therefore moves slowlyover contact 0 while the air is escaping from the cushion. The continuedmovement of the arm finally breaks the field-magnet circuit entirely.The machine thenceases to generate current, and no harm can come fromhandling the conductors in any part of the circuit. In order to put themachine into action again the arm 0 must be moved to its originalposition by hand and held there until the main current being once moreestablished the electro-magnet E will hold its armature and thus lockthe arm in position. hen it is desired to stop the action of the dynamo,it is only necessary to force the armature-latch c away from theelectro-magnet E, the arm 0 performing its functions, as beforedescribed. This may be accomplished by the rod 6 If the dynamo isstopped, the arm acts as before, and must necessarily be used wheneverthe dynamo is set at work, thus insuring thatit shall always be inworking order and ready to operate in case of an emergency.

Having thus described my invention, I claim 1. The combination, with ashunt-wound constant-current dynamo, of a make-andbreak switch locatedin its field-magnet circuit, and in its main circuit an electro-magneticdevice for holding said switch in its closed position, and means foropening the switch when it has been released by said electro-magnet,substantially as described.

2. An automatic safety device for dynamos, consisting of a switch-armincluded in the field-magnet circuit and acted upon by a spring or itsequivalent, in combination with a magnet in the main circuit of thedynamo,

said magnet acting when energized to maintain the switch-arm in itsclosed position,and when de-energized to release the switch-arm andallow the spring to act and break the field-magnet circuit.

3. An automatic safety device for shuntwound dynamos, consisting of aswitch included in the field-magnet circuit, a catch for holding theswitch in its closed condition, a spring acting upon the switch tendingto break the field-magnet circuit, and a second contact-piece in thepath of the switch-arm, said second contact-piece being connected withthe main or first contact through a resistance, as and for the purposeset forth.

4'. An automatic safety device for shuntwound dynamos, consisting of aswitch i11- cluded in the field-magnet circuit, a catch for holding theswitch in its closed condition, a spring acting upon the switch tendingto break the field-magnet circuit, a second contact-piece in the path ofthe switch-arm, said contact-piece being connected. to the main or firstcontact through a resistance, and a retarding device arranged to checkthe motion of the switch-arm while it is passing over the secondcontact, substantially as and for the purpose set forth.

5. An automatic safety device for shuntwound dynamos, consisting of aswitch-arm in the field-magnet circuit and a spring tending to move theswitch-arm to break the circuit, a latch for holding the switch-armclosed, and a magnet in the main circuit for holding the latch inengagement with the switch, as described.

In witness whereof I have hereunto signed my name in the presence of twosubscribing witnesses.

ERNEST I. (,LARK.

lVitnesses:

JAMEs ll. SEYMOUR, WM. A. ROSENBAUM.

